S3 Select vs Athena

It depends on your use-case.

S3 Select allows you to retrieve a subset of data from a single object in S3.

Athena allows you to define tables that represent many objects in S3 and perform aggregations, joins, etc. across tables.

Athena is the service with more features and capabilities, but that doesn't make it a better option if you only need the capabilities of S3 Select.

For example you could use Athena for the same use-case as S3 Select, but then you would have to create tables for each individual object. With S3 Select there are no tables to create, you just specify the object key in the API call. So for such a use case S3 Select would be quicker and less effort.